Aromatic polyamides, because of their excellent properties such as heat resistance, transparency and mechanical properties, are widely used in such fields as textiles, molding materials, composite materials, and electrical and electronic components.
However, in general, aromatic polyamides, owing to intramolecular hydrogen bonding and stacking between the aromatic groups, have large cohesive forces between the molecules and thus a very low solubility in organic solvents. Another problem is that they become insoluble during reaction.
In linear aromatic polyamides, known methods for increasing the solubility include the technique of using a monomer into which flexible structural units such as oxygen, SO2 and methylene groups have been introduced (Patent Document 1), and the technique of using a diamine having a group with a large molecular size, such as a fluorene group (Patent Document 2).
However, it is expected that hyperbranched polymers will generally exhibit a better solubility than linear polymers.
Two approaches are known for preparing such polymers: the AB2 route and the A2+B3 route, “A” and “B” corresponding to functional groups within the monomers.
For example, in the AB2 route, a trifunctional monomer having one functional group A and two functional groups B reacts to give a hyperbranched polymer.
In the A2+B3 route, a monomer having two functional groups A reacts with a monomer having three functional groups B to give a hyperbranched polymer. In this route, in an ideal case, 1:1 adducts of two monomers having only one functional group A and only two functional groups B form, and these adducts further react to give a hyperbranched polymer.
AB2 type polycondensation of a monomer having a carboxylic acid group and an amino group on the molecule (Non-Patent Document 1) and A2+B3 type polycondensation using a benzenetricarboxylic acid and a diamine compound (Non-Patent Document 2) have been reported for such hyperbranched polyamides.
However, in these methods, the loss of solubility is difficult to control and the reactions take a long time.
Moreover, the hyperbranched aromatic polyamide obtained by a technique like that in Non-Patent Document 2 is inadequately soluble in organic solvents.